A power amplifier is an important component of a radio base station, and efficiency of the power amplifier determines parameters such as power consumption, size, and heat design of the base station. Signals with a high peak-to-average ratio, particularly, have a higher requirement for a power amplifier in a base station. In order to amplify these signals with a high peak-to-average ratio without distortion, one of common methods is a power back-off method, that is, a power amplifier operates in an A-type or AB-type state, stays away from a saturation region, and enters a linear operating region, thereby improving linearity of the power amplifier. However, a disadvantage of the method lies in that a dramatic decrease in power amplification efficiency is caused, and under a same output power, energy consumption of a base station is increased greatly.
In order to improve power amplification efficiency when the power back-off method is used for amplifying a signal, the other approaches proposes that an envelope tracking (ET) amplifier and a Doherty amplifier be combined in order to improve power amplification efficiency of a signal with a high peak-to-average ratio under back off using a back-off efficiency advantage of the Doherty amplifier. In the power amplifier, a main power amplifier of the Doherty amplifier is connected to the envelope modulator, the envelope modulator performs ET on the main power amplifier, and at the same time, an auxiliary power amplifier is supplied with power using a fixed voltage. When an amplifier of such a structure operates, a loss of power amplification efficiency is easily caused, thereby having limited improvement in efficiency.